Level 1, level 2 and level 3 are the authors conceptions. Another post of his details what he means... http://www.pathsensitive.com/2018/01/the-three-levels-of-

Level 1, level 2 and level 3 are the authors conceptions. Another post of his details what he means... http://www.pathsensitive.com/2018/01/the-three-levels-of-software-why-code.html?m=1 http://www.pathsensitive.com/2018/01/the-three-levels-of-sof...